The nearest equivalent nowadays are achievements, I think. Some of them are just as challenging.
That's the problem... those achievements are awards instead of rewards.
Achievements can be nice, but can be a problem for some people depending on what the achievement is for. If it's an achievement for self-play, then that's great. It gives you your own personal goal to accomplish. However, when they're related to online multiplayer games, it can be a problem. I've read stories of players complaining about how other players wouldn't take the multiplayer game seriously because they were too focused on earning achievements.
Let's take
Halo 3 as an example. One achievement had something to do with killing a certain number of people by headshots using sniper rifles. Suddenly, there were players who refused to use nothing but sniper rifles and just sat/stood there trying to shoot people in the head while leaving them open targets to the experts to kill them. This lead to messed up team wins.
It's more fun when achievements come with rewards. I had a game for the Xbox called
Black. Beating the game on hard mode unlocked black ops mode. Beating the game on normal or hard mode unlocked silver weapons (unlimited ammo). It was these things that made me want to play the entire game 4 times (easy, normal, hard, & black ops). I felt like a god running around with silver machine gun & grenade launcher combo gun!
I have a friend who plays his games the first time to beat it, then the second time to earn all achievements.
We'd only play Temple and that other one (with silvery walls, can't remember the name of it). Usually Temple. Usually one hit kill slappers only or knives, sometimes automatics, and if my pushy housemate was there he'd often insist on power weapons to get the RC-90 and the rocket launcher. This was in a student house, it was hilarious fun.
When Perfect Dark came out I rushed out in bought it. However, while there were more weapons and things to do, the added complexity of the game and the controls meant the elegant simplicity of Goldeneye was gone and my housemates, none of them hardcore gamers, didn't like it as much,
"silvery walls"? Sounds like the Complex level. That's one of my other favorite levels. It's big, but has a lot of pathways and levels.
Yeah, I played
Perfect Dark a few times. I was looking forward to the
GoldenEye levels that they had brought back, but the gameplay wasn't the same. One thing that made the levels different was that you could walk off the edge, while in
GoldenEye you couldn't.
One nice weapon was the X-Ray Sniper Rail Gun. (I can't remember the exact name for it, but it was nice if I could hide somewhere and shoot anyone anywhere in the level.)
So many games I wanted to play now - I wanted to race iRacing, play little BioShock 1/2 (I bought them through Steam summer sale), and Mass Effect 3 expansion. 
